Gadget Freak Case #253: Peltier Thermopile Cloud Sensor 14309

Peltier, or Thermoelectric, coolers are a fairly modern device, but the concept of generating electricity with dissimilar metals goes back to Seebeck and Peltier's work in the 1800s. Modern devices use alternating P and N semiconductor junctions to pump heat from one side of the device to the other. However, when heat is applied to one side and cold applied to the other, these devices will generate electricity.

NASA has taken advantage of this effect to construct Radioisotope Thermoelectric Generators (RTGs) for its deep-space and planetary missions. Decaying plutonium generates heat, and heat sinks or fins remove the heat. The difference in temperature generates electricity.

My gadget operates by the absorption of heat on one side of the Peltier cooler to sense broadband energy from ultraviolet to the far infrared. It is controlled by a simple op-amp circuit that has adjustable gain and output null. It can, therefore, be used in many applications, just by varying the gain or making slight modifications to the design. This device is able to measure incident energy over a broad spectrum.

The design of this device is divided into two basic components, the circuit and the detector head. The circuit and final construction is very flexible and can be configured in many different ways to best suit the builder. The sensor head can also be designed to use small Peltier devices for small thermal mass and faster response or large ones for capturing large amounts of energy.

Although the primary purpose of this project was to detect clouds, it turned out to be a fairly interesting project for measuring other sources of radiation. It was tested with other optical sources such as lasers and flashlights with equal success and sensitivity. The sensitivity of the sensor is quite amazing. When in close proximity, the heat of one's hand is easily detected. I found this sensor design to be particularly sensitive, easy to fabricate, and a worthwhile endeavor. It is well worthwhile investigating these other uses as well.

Do you have a Gadget Freak project you would like the world to see? Send a brief description of your gadget and a photo to Assistant Managing Editor Lauren Muskett.

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